warning while making cast

[Roman Mashak]

Hello,

given a simple code:

#include <math.h>
long hyp(long height, long base)
{
return sqrt(height * height + base * base);
}

int main(void)
{
long h = hyp(10, 20);
return 0;
}

I compile this on Debian 4.0 (gcc (GCC) 4.1.2 20061115 (prerelease) (Debian
4.1.1-21)):
#gcc -ansi -pedantic -W -Wall -lm hyp.c

As I understand, according to standard sqrt returns double, but we assign
result to long, resulting in information loss. Nevertheless I get no
warning, why is it so?

Hope it's strictly C related question.

With best regards, Roman Mashak.

[vippstar@gmail.com]

Re: warning while making cast

On Jun 6, 6:04 am, "Roman Mashak" <m...@tusur.ruw rote:

Hello,
>
given a simple code:
>
#include <math.h>
long hyp(long height, long base)
{
return sqrt(height * height + base * base);
>
}
>
int main(void)
{
long h = hyp(10, 20);
return 0;
>
}
>
I compile this on Debian 4.0 (gcc (GCC) 4.1.2 20061115 (prerelease) (Debian
4.1.1-21)):
#gcc -ansi -pedantic -W -Wall -lm hyp.c
>
As I understand, according to standard sqrt returns double, but we assign
result to long, resulting in information loss. Nevertheless I get no
warning, why is it so?
>
Hope it's strictly C related question.

The return value of sqrt is implicity converted to long.
6.3.1.4 --
When a finite value of real floating type is converted to an integer
type other than _Bool,
the fractional part is discarded (i.e., the value is truncated toward
zero). If the value of
the integral part cannot be represented by the integer type, the
behavior is undefined.

[Richard Tobin]

Re: warning while making cast

In article <g28h8a$147s$1@ relay.tomsk.ru> , Roman Mashak <mrv@tusur.ruwr ote:

>As I understand, according to standard sqrt returns double, but we assign
>result to long, resulting in information loss. Nevertheless I get no
>warning, why is it so?

Compilers aren't required to warn you about information loss. I would
certainly find it annoying if a compiler did that by default.

I would have expected gcc to warn about it if you specified -Wconversion,
but it doesn't seem to, so you could report that as a bug.

-- Richard

--
In the selection of the two characters immediately succeeding the numeral 9,
consideration shall be given to their replacement by the graphics 10 and 11 to
facilitate the adoption of the code in the sterling monetary area. (X3.4-1963)

[Roman Mashak]

Re: warning while making cast

Hello, vippstar@gmail. com!
You wrote on Thu, 5 Jun 2008 04:27:18 -0700 (PDT):

vThe return value of sqrt is implicity converted to long.
In my understanding implicit conversion is a promotion of types, i.e.
without loss of bits. For instance, float to double

v6.3.1.4 --
vWhen a ?nite value of real ?oating type is converted to an integer
vtype other than _Bool,
vthe fractional part is discarded (i.e., the value is truncated toward
vzero). If the value of
vthe integral part cannot be represented by the integer type, the
vbehavior is unde?ned.
Is this excerpt from C99 standard? I compiled the snippet with -ansi, which
is C90 conformant.

With best regards, Roman Mashak. E-mail: mrv@tusur.ru

[Roman Mashak]

Re: warning while making cast

Hello, Richard!
You wrote on 5 Jun 2008 11:41:34 GMT:

RTCompilers aren't required to warn you about information loss. I would
RTcertainly find it annoying if a compiler did that by default.

By default no, but -Wextra is supposed to report about loss of precision as
well. It does not in this case at least. Perhaps this is more GCC relevant
topic.

RTI would have expected gcc to warn about it if you specified
RT-Wconversion, but it doesn't seem to, so you could report that as a
RTbug.

Compiling with -Wconversion invokes this warning:
warning: passing argument 1 of 'sqrt' as floating rather than integer due to
prototype

But nothing about result of function.

With best regards, Roman Mashak. E-mail: mrv@tusur.ru

[blockstack]

Re: warning while making cast

On Jun 5, 11:03 pm, "Roman Mashak" <m...@tusur.ruw rote:

Hello, Richard!
You wrote  on 5 Jun 2008 11:41:34 GMT:
>
 RTCompilers aren't required to warn you about information loss.  I would
 RTcertainly find it annoying if a compiler did that by default.
>
By default no, but -Wextra is supposed to report about loss of precision as
well. It does not in this case at least. Perhaps this is more GCC relevant
topic.
>
 RTI would have expected gcc to warn about it if you specified
 RT-Wconversion, but it doesn't seem to, so you could report that as a
 RTbug.
>
Compiling with -Wconversion invokes this warning:
warning: passing argument 1 of 'sqrt' as floating rather than integer due to
prototype
>
But nothing about result of function.
>
With best regards, Roman Mashak.  E-mail: m...@tusur.ru

try using -Wtraditional-conversion

[vippstar@gmail.com]

Re: warning while making cast

On Jun 6, 6:54 am, "Roman Mashak" <m...@tusur.ruw rote:

Hello, vipps...@gmail. com!
You wrote on Thu, 5 Jun 2008 04:27:18 -0700 (PDT):
>
vThe return value of sqrt is implicity converted to long.
In my understanding implicit conversion is a promotion of types, i.e.
without loss of bits. For instance, float to double
>
v6.3.1.4 --
vWhen a ?nite value of real ?oating type is converted to an integer
vtype other than _Bool,
vthe fractional part is discarded (i.e., the value is truncated toward
vzero). If the value of
vthe integral part cannot be represented by the integer type, the
vbehavior is unde?ned.
Is this excerpt from C99 standard? I compiled the snippet with -ansi, which
is C90 conformant.

Yes it is, but I believe the same rules apply for C90.

[Keith Thompson]

Re: warning while making cast

"Roman Mashak" <mrv@tusur.ruwr ites:

Hello, vippstar@gmail. com!
You wrote on Thu, 5 Jun 2008 04:27:18 -0700 (PDT):
>
vThe return value of sqrt is implicity converted to long.
>
In my understanding implicit conversion is a promotion of types, i.e.
without loss of bits. For instance, float to double

[...]

I'm afraid your understanding is incorrect.

The promotions that occur for operands of most operators are designed
not to lose information (at least in most cases(?)), but those aren't
the only implicit conversions that can occur. In an assignment or
equivalent (initialization , parameter passing), any arithmetic type
can be implicitly converted to any other arithmetic type. You can
even assign a long double to a char. No diagnostic is required,
though compilers are free to print warnings if they choose.

--
Keith Thompson (The_Other_Keit h) kst-u@mib.org <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

[Jack Klein]

Re: warning while making cast

On Thu, 5 Jun 2008 04:27:18 -0700 (PDT), vippstar@gmail. com wrote in
comp.lang.c:

On Jun 6, 6:04 am, "Roman Mashak" <m...@tusur.ruw rote:

[snip]

The return value of sqrt is implicity converted to long.
6.3.1.4 --
When a ?nite value of real ?oating type is converted to an integer
type other than _Bool,
the fractional part is discarded (i.e., the value is truncated toward
zero). If the value of
the integral part cannot be represented by the integer type, the
behavior is unde?ned.

I assume you're using Foxit for a PDF reader. Surely you've noticed
that it does not handle the single glyph combining the letter
combination "fi" in some documents, including the C standard.

I always do a search and replace of '?' with "fi" before I post a
paste from Foxit.

--
Jack Klein
Home: http://JK-Technology.Com
FAQs for
comp.lang.c http://c-faq.com/
comp.lang.c++ http://www.parashift.com/c++-faq-lite/
alt.comp.lang.l earn.c-c++

http://www.club.cc.cmu.edu/~ajo/docs/FAQ-acllc.html

[akbar]

Re: warning while making cast

On Jun 6, 8:04 am, "Roman Mashak" <m...@tusur.ruw rote:

Hello,
>
given a simple code:
>
#include <math.h>
long hyp(long height, long base)
{
    return sqrt(height * height + base * base);
>
}
>
int main(void)
{
   long h = hyp(10, 20);
   return 0;
>
}
>
I compile this on Debian 4.0 (gcc (GCC) 4.1.2 20061115 (prerelease) (Debian
4.1.1-21)):
#gcc -ansi -pedantic -W -Wall -lm hyp.c
>
As I understand, according to standard sqrt returns double,  but we assign
result to long, resulting in information loss. Nevertheless I get no
warning,  why is it so?
>
Hope it's strictly C related question.
>
With best regards, Roman Mashak.

Hello Roman,

Yes, GCC doesn't show any warning as such even after trying with
multiple warning options.

Please try using Splint tool, it should definetly show return-type-
mismatch warning.

Thanks
Akbar

[Richard Bos]

Re: warning while making cast

Jack Klein <jackklein@spam cop.netwrote:

On Thu, 5 Jun 2008 04:27:18 -0700 (PDT), vippstar@gmail. com wrote in
>

On Jun 6, 6:04 am, "Roman Mashak" <m...@tusur.ruw rote:

>

When a ?nite value of real ?oating type is converted to an integer
type other than _Bool,

>
I assume you're using Foxit for a PDF reader. Surely you've noticed
that it does not handle the single glyph combining the letter
combination "fi" in some documents, including the C standard.

It's not necessarily Foxit. I've seen the same with pastes from Acrobat
Reader, into a newsreader which does not recognise those ligatures.

I always do a search and replace of '?' with "fi" before I post a
paste from Foxit.

You have fioating point types?

Richard

[jaysome]

Re: warning while making cast

On Thu, 5 Jun 2008 20:04:10 -0700, "Roman Mashak" <mrv@tusur.ru >
wrote:

>Hello,
>
>given a simple code:
>
>#include <math.h>
>long hyp(long height, long base)
>{
return sqrt(height * height + base * base);
>}
>
>int main(void)
>{
long h = hyp(10, 20);
return 0;
>}
>
>I compile this on Debian 4.0 (gcc (GCC) 4.1.2 20061115 (prerelease) (Debian
>4.1.1-21)):
>#gcc -ansi -pedantic -W -Wall -lm hyp.c
>
>As I understand, according to standard sqrt returns double, but we assign
>result to long, resulting in information loss. Nevertheless I get no
>warning, why is it so?
>
>Hope it's strictly C related question.
>
>With best regards, Roman Mashak.

The Microsoft Visual C++ 6.0 compiler (circa 1998) gives these
warnings:

Compiling...
hyp.c
hyp.c(4) : warning C4244: 'return' : conversion from 'double ' to
'long ', possible loss of data
hyp.c(9) : warning C4189: 'h' : local variable is initialized but not
referenced

hyp.obj - 0 error(s), 2 warning(s)

PC-lint gives these warnings:

PC-lint for C/C++ (NT) Vers. 8.00u, Copyright Gimpel Software
1985-2006

--- Module: hyp.c (C)
_
return sqrt(height * height + base * base);
hyp.c(4) : Info 747: Significant prototype coercion (arg. no. 1) long
to double
hyp.c(4) : Info 790: Suspicious truncation, integral to float
hyp.c(4) : Warning 524: Loss of precision (return) (double to long)
_
}
hyp.c(11) : Warning 529: Symbol 'h' (line 9) not subsequently
referenced
hyp.c(9) : Info 830: Location cited in prior message

--- Global Wrap-up

Note 900: Successful completion, 5 messages produced
Tool returned code: 0

If you want warnings, you could:

(1) Use Windows and compile with VC++ 6.0 (circa 1998) or even give
the free VC++ Express Editions a try.
(2) Use PC-lint on your code.

--
jaysome

http://www.microsoft.com/express/

http://www.gimpel.com/

[CBFalconer]

Re: warning while making cast

Jack Klein wrote:

>

.... snip ...

>
I assume you're using Foxit for a PDF reader. Surely you've noticed
that it does not handle the single glyph combining the letter
combination "fi" in some documents, including the C standard.
>
I always do a search and replace of '?' with "fi" before I post a
paste from Foxit.

I am using FoxitReader 2.1, which has this fault. I recently
downloaded version 2.5, and have not yet installed it. Do you know
if it fixes that glitch? If not I won't install it.

--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home .att.net>
Try the download section.


** Posted from http://www.teranews.com **

[Richard Tobin]

Re: warning while making cast

In article <pl8h445i08n698 ivr1e7t9kl877t6 8qe06@4ax.com>,
Jack Klein <jackklein@spam cop.netwrote:

>I assume you're using Foxit for a PDF reader. Surely you've noticed
>that it does not handle the single glyph combining the letter
>combination "fi" in some documents, including the C standard.

It has handled it corrrectly. The post you were replying to contained
the unicode characters for the ligatures, encoded in UTF-8. The
problem is presumably that your newsreader (like mine) does not
display UTF-8 correctly.

-- Richard
--
In the selection of the two characters immediately succeeding the numeral 9,
consideration shall be given to their replacement by the graphics 10 and 11 to
facilitate the adoption of the code in the sterling monetary area. (X3.4-1963)

[lawrence.jones@siemens.com]

Re: warning while making cast

Jack Klein <jackklein@spam cop.netwrote:

>
I always do a search and replace of '?' with "fi" before I post a
paste from Foxit.

Unfortunately, the ? might actually be supposed to be "fl" instead. (Or
potentially lots of other things, too, but the C Standard should only
have fi and fl ligatures.)

-- Larry Jones

Good gravy, whose side are you on?! -- Calvin